Printing cathode ray tube apparatus



United States Patent PRINTING CATHODE RAY TUBE APPARATUS Wolfgang K. Berthold, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation,

Nutley, N.J., a corporation of Maryland Filed Sept. 7, 1965, Ser. No. 485,318

US. Cl. 1786.6 Int. Cl. H04n 5 76' 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to printing cathode ray tube apparatus for converting an electrical signal into a corresponding recorded visual image, and more particularly to apparatus for converting and printing black and white information.

In one conventional type of high speed printer, a scanning electron beam of a cathode ray tube is used to excite a phosphor thereby to develop a light image which is optically coupled to a photoconductor to produce charge carriers in the photoconductive material. The resultant charge pattern on the photoconductor is transferred to or from a dielectric media, such as paper, this charge pattern on the dielectric media being rendered visible through conventional xerographic techniques.

Another known method of high speed printing utilizes electrolytic deposition of tellurium by current flow through moistened paper. In that method, premoistened paper is passed overa tellurium platen which is connected to the negative side of a power supply. Needles or pins slide over the opposite side of the paper and when a particular pin is connected to the positive side of the power supply, current flows through the wet paper to the tellurium platen. This current flow electrolytically solves the tellurium from the platen and transports it into the paper, where it remains in a colloidal elementary form as a tiny black dot.

Known photoconductors have long photo-response decay time and relatively low photoresistance. In prior apparatus employing a stationary photoconductor, the photoconductor and the printing media formed a resistance-capacity circuit. In order to make maximum utilization of the bulk photoconductivity of the photoconductor, i.e., to make maximum use of the available charge carriers during the decay time, it is desirable to proportion the impedance of the RC circuit formed by the photoconductor and the printing media so that the RC time constant of the circuit is matched to the photoconductive decay time of the photoconductor. In application Ser. No. 389,281 of the present inventor filed Aug. 13, 1964, now US. Patent No. 3,368,106, and assigned to the assignee of the present application, cathode ray printing tube apparatus is proposed employing a stationary photoconductor arranged so that the direction of charge carrier movement and thus current flow through the photoconductive layer is parallel to its opposite surfaces rather than transverse thereto, thus substantially increasing the resistance of the photoconductor without a corresponding decrease in its intrinsic capacitance. Adjustment of the resistance of the photoconductor to the capacitance of the printing media is thus permitted so that the time constant of the RC circuit may be matched to the decay time of the photoconductor.

Patented Jan. 28, 1969 In the case of high speed printing tubes for printing black and white information, such as printed or typed copy, it is necessary to charge or discharge an element on the printing media to the required voltage in a sequence of black and white dots. This in turn requires that the pre-existing charge condition of an element following a black dot remain unchanged. However, with prior apparatus, the element will lose part of its electrons to refill the capacity of the photoconductor and its metallic connection to the surroundings. Therefore, in addition to the above-described photoconductive decay time, prior apparatus has provided a slow response due to the unavoidable capacity of the photoconductor. In addition, rapid charging or discharging of the printing media has been difficult due to capacitive coupling to adjacent elements, interference due to triboelectric, i.e., static charging by the friction of the printing media with the photoconductor, and other erratic charges. It is, therefore, desirable to provide cathode ray printing tube apparatus in which the influence of the photoconductor capacity and the capacity of the printing media and its speed is diminished and the coupling of adjacent elements and triboelectric effects is reduced.

It is accordingly an object of the invention to provide improved printing cathode ray tube apparatus.

Another object of the invention is to provide improved printing cathode ray tube apparatus in which the influence of photoconductor and printing media capacity and the printing media speed is diminished and the coupling of adjacent elements and triboelectric effects is reduced.

-In' accordance with the broader aspects of the invention, a cathode ray tube is provided having faceplate means with inner and outer surfaces and means for forming and directing an electrom beam toward the faceplate means, including means for repetitively scanning the beam in a first direction across the faceplate means; and means for deflecting the beam in a second direction at right angles to the first direction between first and second positions on the faceplate means in response to the levels of a bilevel video signal. Relatively thin variable resistance means is provided having opposite surfaces and two spaced opposite peripheral edges, the variable resistance means having one of its surfaces closely adjacent and parallel with one of the faceplate means surfaces and its opposite edges extending in the first direction. The variable resistance means is of the type which has the resistance of an incremental area thereof variable from a relatively high to a relatively low value in response to direction of the electron beam toward a corresponding incremental area on the faceplate means; and the variable resistance means is arranged so that the first and second beam positions are intermediate its opposite edges. First and second electrode means are respectively coupled to the variable resistance means adjacent its opposite edges and third electrode means is coupled to the variable resistance means intermediate the first and second beam positions, the third electrode means thus definine first and second sections of the variable resistance means respectively between the third electrode means and the first and second electrode means. The first and second variable resistance means sections thus respectively have incremental areas thereon which correspond to the first and second beam positions, and the third electrode means has a printing portion which defines a gap with fourth electrode means in which a sheet of dielectric printing material is positioned. A first source of potential is coupled across the first and fourth electrodes and a second source of potential is coupled across the second and fourth electrodes, one of the sources being proportioned to change the pre-existing charge condition on the sheet in the gap in response to direction of the beam toward the incremental area of the respective one of the variable resistance means sections and the other of the sources being proportioned to maintain a pre-existing charge condition on the sheet in the gap in response to direction of the beam toward the incremental area of the other of the variable resistance means sections, a charge image thus being impressed on the sheet in the gap responsive to the positions of the beam.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side schematic view, partly in cross-section, showing one embodiment of the printing cathode ray tube apparatus of the invention;

FIG. 2 is a fragmentary cross-sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a schematic diagram showing a simplified equivalent circuit of one of the photoconductive elements of the apparatus of FIGS. 1 and 2;

FIG. 4 is a fragmentary cross-sectional view showing another embodiment of the invention; and

FIG. 5 is a fragmentary cross-sectional view showing yet another embodiment of the invention.

Referring now to FIGS. 1 and 2 of the drawings, the printing tube apparatus of the invention, generally indicated at 10, comprises a cathode ray tube 11 having an evacuated envelope 12 with a faceplate end 13. In the illustrated embodiment wherein scanning in one direction, as shown by the arrows 14, is accomplished by movement of the printing paper 15, as will be hereinafter more fully described, and thus in which it is only required that the electron beam be scanned in one direction at right angles to the direction of movement 14 of the printing paper, as shown by the arrow 16, the envelope 12 is flattened to provide the faceplate end 13 with an elongated cross-sectional configuration in order to reduce space requirements.

A conventional electron gun 17 is positioned within envelope 12 and having conventional electrodes (not shown) for forming and directing electron beam 18 toward faceplate 13. Beam 18 is repetitively scanned over faceplate 13 in the direction shown by the arrow 16 by means of conventional deflection electrodes 19 coupled to a conventional line sweep generator 20.

The printing cathode ray tube of the invention is used for converting a bilevel video signal contained black and white information to corresponding black and white visual information recorded on the printing paper 15. In accordance with the invention, the electron beam 18 is deflected at right angles to the scanning direction 16 between first and second positions 22, 23 on the faceplate .13 by means of conventional deflection electrodes 122 in response to the two levels of the input signal, deflection electrodes 122 being coupled to input circuit 24 which is adapted to receive the bilevel input video signal. Thus, as the beam 18 is scanned in direction 16 across the faceplate 13, it will be deflected to position 22 in response to a black level input video signal and to position 23 in response to the white level input video signal, as shown in dashed lines in FIG. 2.

In the illustrated embodiment, the faceplate 13 comprises an elongated fiber-optic sheet 21 sealed, as by means of a glass frit seal, to the open end of envelope 12. It will be understood that the fiber-optic material from which sheet 21 is formed is not a part of the present invention, such fiber-optic materials being well known to those skilled in the art. Optical fibers are essentially smalldiameter rods of transparent dielectric material, such as 1 to 2 mil diameter glass fibers. Light conduction along transparent rods is well known, and when a large number of such rods or fibers are sealed together in the form of a sheet having flat opposite sides and with the fibers extending transversely between the sides, an optical image is transmitted from one side to the other with high light efficiency. As seen in FIG. 1, the optical fibers forming sheet 25 extend generally transversely between the opposite surfaces of the sheet.

The inner surface of the fiber-optic sheet 21 is coated with a layer 31 of a suitable high-resolution phosphor. It will be readily understood that in order to increase the brightness of the optical image produced in the phosphor layer 31 in response to impingement of the electron beam 18 thereon, and also to increase the resistance to ion bombardment, a thin aluminum film may be deposited on the surface of the phosphor layer 31, as is well known to those skilled in the art. It will now be seen that the optical or light image produced in the phosphor layer 31 in response to impingement by the electron beam 18 will be transmitted by the fiber-optic sheet 21 to its outer surface with minimum loss of resolution.

In accordance with the invention, a plurality of pairs of members 25, 26 of photoconductive material are provided abutting the outer surface of the fiber-optic sheet 21. Each of the pairs of photoconductive members 25, 26 is closely spaced-apart in the direction 14 and is likewise closely spaced-apart from adjacent pairs of members in the direction 16, suitable layers 27 of insulating material preferably spacing the respective pairs of photoconductive members 25, 26. An electrode 28 elongated in the direction 16 contacts the upper ends 29 of the photoconductive members 25 and another electrode 30 elongated in the direction 16 contacts the lower ends 32 of the photoconductive members 26, electrodes 28, 30 thus being spaced-apart in the direction 14.

A plurality of printing electrodes 33 are provided positioned between respective pairs of photoconductive members 25, 26 and respectively contacting the lower ends 34 of the photoconductive member 25 and the upper ends 35 of the photoconductive members 26. Electrodes 33 are thus closely spaced-apart along a line extending in the direction 16. Each of the printing electrodes 33 has a printing portion 36 extending outwardly from the photoconductive members 25, 26 and defining a gap with electrode 37 through which the printing paper 15 is drawn.

Reference to FIG. 2 will now reveal that the light image provided by the phosphor layer 26 in response to impingement of the electron beam 18 in its lower position 22 will impinge upon the photoconductive members 26 intermediate printing electrodes 33 and the elongated electrode 30, and that the light image provided by the phosphor layer 26 in response to impingement by the electron beam 18 in its upper position 23 will impinge upon the photoconductive members 25 intermediate the printing electrodes 33 and the elongated electrode 28. It is thus seen that one of the photoconductive members 25, 26 will always be illuminated in response to the electron beam 18, the beam 18 being deflected in direction 14 by the printing information contained in the bilevel input video signal. It will be readily understood that the electron beam 18 provided by the electron gun 17 is a constant current, wellfocused beam. The shape of the beam is desirably rectangular for optimum response in the photoconductor, the beam preferably substantially covering the respective strip 25 or 26.

The sheet 15 of printing paper is drawn from a supply roll 38 through the gap defined between the printing portions 36 of printing electrodes 33 and electrode 37 by a suitable pickup roll 39, the sheet of printing paper 15 with the electrostatic charge image thereon passing through conventional toner and fixer apparatus 40, 42 in order to develop the latent charge image thereon and to render it visible in black and white form. It will be readily understood that the photoconductive members 25, 26 have high dark resistance which is reduced to a much lower value in response to impingement of light thereon from the phosphor layer 31. It will also be readily seen that by virtue of the spacing of the elongated electrodes 28, 30 from the printing electrodes 33 in a direction parallel to the surface of faceplate 13 and at right angles to the scanning direction 16 of the electron beam 18, the direction of charge carrier movement and thus, current flow through the photoconductive members 25, 26 is parallel to their opposite surfaces rather than transverse thereto, and thus, that the photoresistance of the photoconductive members 25, 26 is substantially increased without a corresponding increase in their intrinsic capacitance.

Referring now to FIG. 3 in which a single pair of photoconductive members 25, 26 is schematically shown, in accordance with the invention, a first source of direct current potential, shown here as being a battery 43, is coupled between electrode 37 and the elongated electrode 28 and a second source of direct current potential, shown here as being a battery 44, is coupled between electrode 37 and the elongated electrode 30. In the illustrated embodiment in which sheet of printing paper is not precharged, and in which, accordingly, a charge is placed on the paper in response to black signal information, source 43 is of sufliciently high potential, such as +300 volts, to charge the sheet 15 when the photoconductive member 26 is illuminated, whereas source 44 has a suitable potential, such as -25 volts, to maintain the sheet 15 uncharged when the photoconductive member 25 is illuminated. If, on the contrary, the sheet of printing paper 15 were precharged and accordingly discharged to provide white information, source 43 would be proportioned and polarized to retain the previous charge condition on the sheet of printing paper 15 in response to illumination of photoconductive member 26, while source 44 would be'proportioned and polarized to discharge the sheet of printing paper 15 in response to illumination of photoconductive member 25.

Inspection of FIG. 3 will reveal that the gap defined between printing portion 36 of the printing electrode 33 and electrode 37 forms a capacitor with the printing paper 15 being the dielectric, the intrinsic capacitance of the photoconductive members 25, 26 being indicated schematically at 25c, 26c. It will be seen that the provision of two photoconductive members 25, 26 for each photoconductive element, one of which is at all times illuminated, and the provision of the additional potential source coupled to the photoconductive element which maintains the preestablished charged condition on the sheet of printing paper 15, i.e., ground in the case of paper which has not been precharged and the charge condition in the case of precharged paper, eliminates the above-described problem of the tendency of the printing paper to refill the capacity of the photoconductor and the capacity of adjacent elements, and also the effect of triboelectric charging, whereupon a transition from a black element to a white element may be rapidly accomplished.

It will further be observed that the charging voltage applied to each printing electrode 33 depends only upon the ratio of the resistance of the two photoconductive members 25, 26 to which it is connected, and not upon the absolute resistance value of either photoconductive member. This further permits variations of photoconductive sensitivity from one end of the printing line to the other as long as adjacent photoconductive elements remain similar. Referring now to FIG. 4, this characteristic permits the provision of a single relatively thin homogeneous layer 45 of photoconductive material in lieu of the separate photoconductive elements respectively formed of the photoconductive members 25, 26 described above in connection with FIGS. 1 and 2. Here, the photoconductive layer 45 which is elongated in the direction 16 may be deposited directly upon the outer surface of the fiber-optic sheet 21 with the elongated electrodes 28, 30 being evaporated thereon in accordance with conventional techniques. In this embodiment, a plurality of contact wires 46 are provided in lieu of the printing electrodes 33 of the previous embodiment, contact wires 46 respective ly making contact with the photoconductive layer 45 and being closely spaced-apart in a line extending in the direction 16. This arrangement will further decrease the delay time considerably. The resistance of photoconductivity will retain the information in any photoconductive element until the electron beam 18 returns for the next scan, and thus, if one element is assumed to hold substantially percent of its photoconductivity until the next scan line, the potential would still be reduced to 50 percent if the opposite element is rendered conductive on the next successive scan.

Referring now brifly to FIG. 5, it will be seen that the invention described above is equally applicable to the employment of material having its resistance varied by electron bombardment-induced conductivity rather than by photoconductivity as in the case of the previous embodiments. Thus, an elongated relatively thin layer 47 of electron bombardment-induced conductivity material may be deposited on the inner surface of faceplace 13 of the envelope 11 and having the elongated electrodes 28, 30 contacting its peripheral edges, and a plurality of discrete printing electrodes 48 may be provided contacting the layer 47 and being closely spaced-apart in a line extending in the direction 16.

Referring again to FIG. 3, in order to improve the con tact of the printing portions 36 of the printing electrodes 33, 46 or 48 with the sheet of printing paper 15, it may be advantageous to apply a high frequency alternating current potential, such as 100 kilocycles per second, between the printing portions 36 and the backing electrode 37. To accomplish this, a suitable transformer 49 is provided having a secondary Winding coupled in series with electrode 37 and having its primary winding coupled to a suitable signal generator 50. By this means, a gas discharge is initiated between the respective printing portion 36 and the surface of the sheet of printing paper 15 permitting a charge deposition on the paper without direct contact of the printing portion 36 with the surface of the paper.

While the invention has been illustrated and described above in connection with printing apparatus of the electrostatic type, it will be readily apparent that it is equally applicable to other high speed printing methods, such as the electrolytic method above-described.

While there have been described above the principles of this invention in connection with specific apparatus, it is to the clearly understood that this description is made only by way of example and not as a limitation to the scope of this invention.

What is claimed is:

1. Apparatus for converting a bilevel video signal into a corresponding black and white image recorded on a dielectric sheet, said apparatus comprising: a cathode ray tube having faceplate means with inner and outer surfaces, means for forming and directing an electron beam toward said faceplate means including means for repetitively scanning said beam in a first direction across said faceplate means and means for deflecting said beam in a second direction at right angles to said first direction between first and second positions on said faceplate means in response to the levels of said video signal, respectively; relatively thin variable resistance means having opposite surfaces and two spaced opposite peripheral edges; said resistance means having one of said surfaces closely adjacent and parallel with one of the surfaces of said faceplate means and said edges parallell with said first direction; said resistance means having the resistance of an incremental area thereof variable from a relatively high to a relatively low value in response to direction of said beam toward a corresponding incremental area on said faceplate means, said first and second beam positions being intermediate said edges; first and second electrode means coupled to said resistance means respectively adjacent said edges; third electrode means coupled to said resistance means intermediate said first and second beam positions thereby defining first and second sections of said resistance means respectively between said third electrode means and said first arid second electrode means; said first and second resistance means sections respectively having incremental areas thereon corresponding to said first and second beam positions, said third electrode means having a printing portion; and fourth electrode means defining a gap with said printing portion for receiving a sheet of printing material; a first source of potential coupled across said first and fourth electrodes and a second source of potential coupled across said second and fourth electrodes, one of said sources being proportioned to change the pre-existing charge condition in said gap in response to direction of said beam toward the incremental area of a respective one of said resistance means sections and the other of said sources being proportioned to maintain the pre-existing charge condition in said gap in response to direction of said beam toward the incremental area of the other of said resistance means sections whereby a charge image is impressed across said gap responsive to the positions of said beam.

2. The apparatus of claim 1 wherein said resistance means comprises a homogeneous layer of resistance material elongated in said first direction, said first and second electrode means being elongated in said first direction, and wherein said third electrode means comprises a plurality of discrete electrode elements closely spaced-apart on a line parallel with said first direction, each of said electrode elements having a portion defining a gap with said fourth electrode means.

3. The apparatus of claim 1 wherein said resistance means comprises a plurality of resistance elements respectively elongated in said second direction and closely spaced-apart in said first direction; wherein said first and second electrode means are elongated in said first direction; and wherein said third electrode means comprises a plurality of discrete electrode elements respectively connected to said resistance elements; each of said electrode elements having a portion defining a gap with said fourth electrode means.

4. The apparatus of claim 1 wherein said resistance means is formed of photoconductive material and is closely adjacent the outer surface of said faceplate means; and wherein the inner surface of said faceplate means has a phosphor display screen closely adjacent thereto Whereby variation of the resistance of said resistance means is responsive to light generated by said phosphor display screen in response to impingement of said beam thereon.

5. The apparatus of claim 1 wherein said resistance means is formed of electron bombardment-induced conductivity material and is closely adjacent the inner surface of said faceplate means whereby variation of the resistance of said resistance means is responsive to impingement of said beam thereon.

6. The apparatus of claim 1 further comprising a source of high frequency alternating current potential coupled in circuit with said third and fourth electrode means.

7. The apparatus of claim 1 wherein said resistance means comprises a relatively thin homogeneous layer of photoconductive material abutting the outer surface of said faceplate means and elongated in said first direction, said first and second electrode means being elongated in said first direction; wherein said third electrode means comprises a plurality of discrete electrode elements closely spaced-apart on a line extending in said first direction; each of said electrode elements having a portion defining a gap with said fourth electrode means; and wherein the inner surface of said faceplate means has a phosphor display screen deposited thereon whereby variation of the resistance of said resistance means is responsive to light generated in said phosphor display screen in response to impingement of said beam thereon.

8. The apparatus of claim 1 wherein said resistance means comprises a plurality of relatively thin resistance elements abutting the outer surface of said faceplate means and respectively elongated in said second direction; each of said resistance elements comprising first and second resistance members formed of photoconductive material and closely spaced-apart in said second direction, said first and second members of said elements respectively defining said first and second resistance means sections; wherein said first and second electrode means are elongated in said first direction and respectively contact the opposite edges of said resistance elements, wherein said third electrode means comprises a plurality of electrode elements disposed in a line extending in said first direction respectively positioned between said first and second resistance members and contacting the same; each of said electrode elements having a portion defining a gap with said fourth electrode means; and wherein the inner surface of said faceplate means has a phosphor display screen deposited thereon whereby variation of the resistance of said resistance means is responsive to light generated in said phosphor display screen in response to impingement of said ibeam thereon.

9. The apparatus of claim 1 wherein said resistance means comprises a homogeneous layer of electron bombardment-induced conductivity material deposited on the inner surface of said faceplate means and elongated in said first direction; said first and second electrode means being elongated in said first direction; and wherein said third electrode means comprises a plurality of discrete electrode elements closely spaced-apart on a line extending in said first direction; each of said electrode elements having a portion extending through said faceplate means and defining a gap with said fourth electrode means whereby variation of the resistance of said resistance means is responsive to impingement of said beam thereon.

References Cited UNITED STATES PATENTS 3,277,237 10/1966 Wolfgang 178-66 3,283,069 11/1966- MacGrilf 1786.6 3,301,947 1/1967 Stone 178-6.6 3,368,106 2/1968 Berthold 178-6.6

ROBERT L. GRIFFIN, Primary Examiner. H. W. BRITTON, Assistant Examiner.

US. Cl. X.R. 

